scholarly journals Purinergic activation of anion conductance and osmolyte efflux in cultured rat hippocampal neurons

2008 ◽  
Vol 295 (6) ◽  
pp. C1550-C1560 ◽  
Author(s):  
Guangze Li ◽  
James E. Olson
Keyword(s):  
Mammalian Cells ◽  
Hippocampal Neurons ◽  
Regulatory Volume Decrease ◽  
Extracellular Atp ◽  
Cell Swelling ◽  
Nucleotide Receptors ◽  
Organic Osmolytes ◽  
Anion Channels ◽  
Critical Signal ◽  
Current Activation

The majority of mammalian cells demonstrate regulatory volume decrease (RVD) following swelling caused by hyposmotic exposure. A critical signal initiating RVD is activation of nucleotide receptors by ATP. Elevated extracellular ATP in response to cytotoxic cell swelling during pathological conditions also may initiate loss of taurine and other intracellular osmolytes via anion channels. This study characterizes neuronal ATP-activated anion current and explores its role in net loss of amino acid osmolytes. To isolate anion currents, we used CsCl as the major electrolyte in patch electrode and bath solutions and blocked residual cation currents with NiCl2 and tetraethylammonium. Anion currents were activated by extracellular ATP with a Km of 70 μM and increased over fourfold during several minutes of ATP exposure, reaching a maximum after 9.0 min (SD 4.2). The currents were blocked by inhibitors of nucleotide receptors and volume-regulated anion channels (VRAC). Currents showed outward rectification and inactivation at highly depolarizing membrane potentials, characteristics of swelling-activated anion currents. P2X agonists failed to activate the anion current, and an inhibitor of P2X receptors did not block the effect of ATP. Furthermore, current activation was observed with extracellular ADP and 2-(methylthio)adenosine 5′-diphosphate, a P2Y1 receptor-specific agonist. Much less current activation was observed with extracellular UTP, suggesting the response is mediated predominantly by P2Y1 receptors. ATP caused a dose-dependent loss of taurine and alanine that could be blocked by inhibitors of VRAC. ATP did not inhibit the taurine uptake transporter. Thus extracellular ATP triggers a loss of intracellular organic osmolytes via activation of anion channels. This mechanism may facilitate neuronal volume homeostasis during cytotoxic edema.

More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels

2019 ◽  
Vol 400 (11) ◽  
pp. 1481-1496 ◽  
Author(s):  
Lingye Chen ◽  
Benjamin König ◽  
Tianbao Liu ◽  
Sumaira Pervaiz ◽  
Yasmin S. Razzaque ◽  
...  
Keyword(s):  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Anion Channel ◽  
Therapy Resistance ◽  
Cell Swelling ◽  
Organic Osmolytes ◽  
Anion Channels ◽  
Relief Valve ◽  
Wide Range ◽  
And Migration

Abstract The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.

Swelling-activated anion conductance in skate hepatocytes: regulation by cell Cl- and ATP

1996 ◽  
Vol 270 (1) ◽  
pp. C57-C66 ◽  
Author(s):  
P. S. Jackson ◽  
K. Churchwell ◽  
N. Ballatori ◽  
J. L. Boyer ◽  
K. Strange
Keyword(s):  
Mammalian Cells ◽  
Anion Channel ◽  
Fold Increase ◽  
Cation Binding ◽  
Cell Swelling ◽  
Organic Osmolytes ◽  
Main Function ◽  
Anion Conductance ◽  
Cation Permeability ◽  
Current Activation

Cell swelling activates an outwardly rectifying anion conductance in mammalian cells. The channel responsible for this conductance mediates volume-regulatory efflux of organic osmolytes such as taurine. We observed a similar conductance in hepatocytes from the skate Raja erinacea. Whole cell Cl- conductance was increased > 100-fold by a 2-fold increase in hepatocyte volume. The conductance was outwardly rectifying and had a relative cation permeability of approximately 0.2. Cation permeability was increased by reductions in patch pipette CsCl concentration, suggesting that the channel pore contains saturable anion and cation binding sites with different anion and cation affinities. The conductance had a broad anion selectivity and a relative taurine permeability of 0.17. Activation of the conductance required intracellular ATP or a nonhydrolyzable ATP analogue. Elevation of intracellular Cl- from 20 to 155 mM reduced current activation while the rate and extent of cell swelling were unaffected. Reduction of intracellular Cl- concentration to 5-10 mM caused spontaneous current activation without cell swelling. These results suggest that increases in cell Cl- levels increase the volume set point of the channel. We propose that the main function of the outwardly rectifying anion channel is nonselective transport of organic solutes.

scholarly journals Alanine uptake activates hepatocellular chloride channels

1997 ◽  
Vol 273 (4) ◽  
pp. G849-G853 ◽  
Author(s):  
Steven D. Lidofsky ◽  
Richard M. Roman
Keyword(s):  
Amino Acid ◽  
Mammalian Cells ◽  
Chloride Channels ◽  
Amino Acid Uptake ◽  
Experimental Models ◽  
Cell Swelling ◽  
Acid Uptake ◽  
Adaptive Responses ◽  
Anion Channels

Cells involved in the retrieval and metabolic conversion of amino acids undergo significant increases in size in response to amino acid uptake. The resultant adaptive responses to cell swelling are thought to include increases in membrane K+ and Cl− permeability through activation of volume-sensitive ion channels. This viewpoint is largely based on experimental models of hypotonic swelling, but few mammalian cells experience hypotonic challenge in vivo. Here we have examined volume regulatory responses in a physiological model of cell-swelling alanine uptake in immortalized hepatocytes. Alanine-induced cell swelling was followed by a decrease in cell volume that was temporally associated with an increase in membrane Cl− currents. These currents were dependent both on alanine concentration and Na+, suggesting that currents were stimulated by Na+-coupled alanine uptake. Cl− currents were outwardly rectifying, exhibited an anion permeability sequence of I− > Br− > Cl−, and were inhibited by the Cl− channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid, features similar to those reported for a widely distributed class of volume-sensitive anion channels evoked by experimental hypotonic stress. These findings suggest that volume-sensitive anion channels participate in adaptive responses to amino acid uptake and provide such channels with a new physiological context.

Taurine transport in skate hepatocytes. II. Volume activation, energy, and sulfhydryl dependence

1992 ◽  
Vol 262 (3) ◽  
pp. G451-G460 ◽  
Author(s):  
N. Ballatori ◽  
J. L. Boyer
Keyword(s):  
Plasma Membrane ◽  
Concentration Gradient ◽  
Regulatory Volume Decrease ◽  
Metabolic Inhibitors ◽  
Cell Swelling ◽  
Disulfonic Acid ◽  
Organic Osmolytes ◽  
Taurine Transport ◽  
Taurine Concentration ◽  
Taurine Efflux

Isolated skate (Raja erinacea) hepatocytes swollen in hypotonic media exhibited a regulatory volume decrease (RVD) that was associated with only a small increase in K+ or 86Rb+ efflux but a substantial increase in the release of taurine, an amino acid found in high concentrations in skate hepatocytes. Taurine efflux was stimulated in media made hypotonic by addition of H2O or removal of NaCl, as well as in cells swollen in isotonic media containing rapidly penetrating solutes (202 mM ethylene glycol or 202 mM additional urea substituted for 101 mM NaCl), suggesting that cell swelling rather than hyposmolarity is the stimulus for the activation of taurine release. In contrast, release of glutathione, L-[14C]alanine and other alpha-amino acids (e.g., threonine, serine, glutamate, glutamine, glycine, or valine) was unaffected by dilution with 40% H2O. Taurine efflux was not altered by replacement of extracellular Na+ with choline+ or K+ and was only slightly diminished by replacing Cl- with NO3-. Addition of 50 mM taurine or hypotaurine to the incubation media also had no effect on volume-stimulated [14C]taurine efflux, suggesting that the taurine concentration gradient across the plasma membrane is not the driving force. Volume-stimulated taurine transport was temperature sensitive, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibitable (0.5 mM), and nearly completely blocked by metabolic inhibitors (2,4-dinitrophenol, KCN, sodium azide, oligomycin, carbonyl cyanide m-chlorophenylhydrazone, and antimycin A), suggesting an active energy-dependent process. Sulfhydryl-reactive reagents (N-ethylmaleimide, diamide, iodoacetate, tert-butyl hydroperoxide, and mercury) also blocked volume-stimulated taurine efflux, whereas efflux was unaffected by Ca2+ ionophore, phorbol ester, dibutyryl-adenosine 3',5'-cyclic monophosphate, vasopressin, or pretreatment with ouabain or furosemide. N-ethylmaleimide, diamide, 2,4-dinitrophenol, and iodoacetate plus KCN also inhibited the RVD. These findings suggest that, in contrast to hepatocytes from most vertebrate species, RVD in skate hepatocytes is associated with the release of only a small fraction of intracellular K+ but a substantial fraction of intracellular taurine and perhaps other organic osmolytes. This volume-activated taurine transport mechanism is energy and sulfhydryl group dependent and is not related to the taurine concentration gradient across the skate hepatocyte plasma membrane.

scholarly journals Acid- and Volume-Sensitive Chloride Currents in Microglial Cells

2019 ◽  
Vol 20 (14) ◽  
pp. 3475 ◽  
Author(s):  
Michael Kittl ◽  
Katharina Helm ◽  
Marlena Beyreis ◽  
Christian Mayr ◽  
Martin Gaisberger ◽  
...  
Keyword(s):  
Cell Volume ◽  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Cell Volume Regulation ◽  
Cell Types ◽  
Microglial Cells ◽  
Cell Swelling ◽  
Mean Cell Volume ◽  
Current Activation ◽  
And Migration

Many cell types express an acid-sensitive outwardly rectifying (ASOR) anion current of an unknown function. We characterized such a current in BV-2 microglial cells and then studied its interrelation with the volume-sensitive outwardly rectifying (VSOR) Cl− current and the effect of acidosis on cell volume regulation. We used patch clamp, the Coulter method, and the pH-sensitive dye BCECF to measure Cl− currents and cell membrane potentials, mean cell volume, and intracellular pH, respectively. The ASOR current activated at pH ≤ 5.0 and displayed an I− > Cl− > gluconate− permeability sequence. When compared to the VSOR current, it was similarly sensitive to DIDS, but less sensitive to DCPIB, and insensitive to tamoxifen. Under acidic conditions, the ASOR current was the dominating Cl− conductance, while the VSOR current was apparently inactivated. Acidification caused cell swelling under isotonic conditions and prevented the regulatory volume decrease under hypotonicity. We conclude that acidification, associated with activation of the ASOR- and inactivation of the VSOR current, massively impairs cell volume homeostasis. ASOR current activation could affect microglial function under acidotoxic conditions, since acidosis is a hallmark of pathophysiological events like inflammation, stroke or ischemia and migration and phagocytosis in microglial cells are closely related to cell volume regulation.

Stimulation by caveolin-1 of the hypotonicity-induced release of taurine and ATP at basolateral, but not apical, membrane of Caco-2 cells

2006 ◽  
Vol 290 (5) ◽  
pp. C1287-C1296 ◽  
Author(s):  
Nina Ullrich ◽  
Adrian Caplanusi ◽  
Bert Brône ◽  
Diane Hermans ◽  
Els Larivière ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Regulatory Volume Decrease ◽  
Protective Mechanism ◽  
Organic Osmolytes ◽  
Wild Type ◽  
Caveolin 1 ◽  
Water Efflux ◽  
Electrophysiological Characterization

Regulatory volume decrease (RVD) is a protective mechanism that allows mammalian cells to restore their volume when exposed to a hypotonic environment. A key component of RVD is the release of K+, Cl−, and organic osmolytes, such as taurine, which then drives osmotic water efflux. Previous experiments have indicated that caveolin-1, a coat protein of caveolae microdomains in the plasma membrane, promotes the swelling-induced Cl− current ( ICl,swell) through volume-regulated anion channels. However, it is not known whether the stimulation by caveolin-1 is restricted to the release of Cl− or whether it also affects the swelling-induced release of other components, such as organic osmolytes. To address this problem, we have studied ICl,swell and the hypotonicity-induced release of taurine and ATP in wild-type Caco-2 cells that are caveolin-1 deficient and in stably transfected Caco-2 cells that express caveolin-1. Electrophysiological characterization of wild-type and stably transfected Caco-2 showed that caveolin-1 promoted ICl,swell, but not cystic fibrosis transmembrane conductance regulator currents. Furthermore, caveolin-1 expression stimulated the hypotonicity-induced release of taurine and ATP in stably transfected Caco-2 cells grown as a monolayer. Interestingly, the effect of caveolin-1 was polarized because only the release at the basolateral membrane, but not at the apical membrane, was increased. It is therefore concluded that caveolin-1 facilitates the hypotonicity-induced release of Cl−, taurine, and ATP, and that in polarized epithelial cells, the effect of caveolin-1 is compartmentalized to the basolateral membrane.

scholarly journals Regulatory volume decrease in carp red blood cells: mechanisms and oxygenation-dependency of volume-activated potassium and amino acid transport

1995 ◽  
Vol 198 (1) ◽  
pp. 155-165 ◽  
Author(s):  
F Jensen
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Regulatory Volume Decrease ◽  
Cell Swelling ◽  
Organic Osmolytes ◽  
Osmotic Swelling ◽  
Original Cell ◽  
Sufficient Stimulus ◽  
K Release ◽  
Volume Decrease

Hypo-osmotic swelling of carp red blood cells (RBCs) induced a regulatory volume decrease (RVD), which restored the original cell volume within 140 min in oxygenated RBCs, whereas volume recovery was incomplete in deoxygenated RBCs. The complete RVD in oxygenated RBCs resulted from a sustained volume-activated release of K+, Cl- and amino acids (AAs). In the absence of ouabain, the cells also lost Na+ as released K+ was partially regained via the Na+/K+ pump. Inorganic osmolytes contributed approximately 70 %, and organic osmolytes approximately 30 %, to the RVD of oxygenated RBCs. Oxygenation in isotonic medium per se activated a K+ efflux from the RBCs. Hypo-osmotic cell swelling stimulated an additional K+ release. The oxygenation-activated and the volume-activated K+ efflux were both inhibited by DIDS and by the replacement of Cl- with NO3-, showing that both types of K+ efflux were Cl--dependent and probably occurred via the same K+/Cl- cotransport mechanism. Once activated by oxygenation, the K+/Cl- cotransport was further stimulated by cell swelling. Deoxygenation inactivated the oxygenation-induced Cl--dependent K+ release and cell swelling was not a sufficient stimulus to reactivate it significantly. In deoxygenated RBCs, the volume-induced K+ release was transient and primarily Cl--independent and, in the absence of ouabain, the cell K+ content recovered towards control values via the Na+/K+ pump. The Cl--independent K+ efflux seemed to involve K+/H+ exchange, but other transport routes also participated. Swelling-activated AA release differed in kinetics between oxygenated and deoxygenated RBCs but was important for RVD at both oxygenation degrees. Approximately 70 % of the AA release was inhibited by DIDS and substitution of NO3- for Cl- produced a 50 % inhibition, suggesting that the AA permeation was partly Cl--dependent. In oxygenated RBCs, a reduction in pH lowered the volume-activated Cl--dependent K+ efflux but not the AA efflux. In deoxygenated RBCs, the acute volume-stimulated K+ and AA release were both increased by acidification. The data are discussed in relation to possible transducer mechanisms and physiological implications.

The volume-regulated anion channel is formed by LRRC8 heteromers – molecular identification and roles in membrane transport and physiology

2015 ◽  
Vol 396 (9-10) ◽  
pp. 975-990 ◽  
Author(s):  
Tobias Stauber
Keyword(s):  
Cell Biology ◽  
Regulatory Volume Decrease ◽  
Anion Channel ◽  
Cell Swelling ◽  
Transepithelial Transport ◽  
Organic Osmolytes ◽  
Physiological Processes ◽  
Starting Point ◽  
And Migration ◽  
Volume Decrease

Abstract Cellular volume regulation is fundamental for numerous physiological processes. The volume-regulated anion channel, VRAC, plays a crucial role in regulatory volume decrease. This channel, which is ubiquitously expressed in vertebrates, has been vastly characterized by electrophysiological means. It opens upon cell swelling and conducts chloride and arguably organic osmolytes. VRAC has been proposed to be critically involved in various cellular and organismal functions, including cell proliferation and migration, apoptosis, transepithelial transport, swelling-induced exocytosis and intercellular communication. It may also play a role in pathological states like cancer and ischemia. Despite many efforts, the molecular identity of VRAC had remained elusive for decades, until the recent discovery of heteromers of LRRC8A with other LRRC8 family members as an essential VRAC component. This identification marks a starting point for studies on the structure-function relation, for molecular biological investigations of its cell biology and for re-evaluating the physiological roles of VRAC. This review recapitulates the identification of LRRC8 heteromers as VRAC components, depicts the similarities between LRRC8 proteins and pannexins, and discussed whether VRAC conducts larger osmolytes. Furthermore, proposed physiological functions of VRAC and the present knowledge about the physiological significance of LRRC8 proteins are summarized and collated.

Regulatory volume decrease in perfused proximal nephron: evidence for a dumping of cell K+

1987 ◽  
Vol 252 (5) ◽  
pp. F933-F942 ◽  
Author(s):  
K. L. Kirk ◽  
D. R. DiBona ◽  
J. A. Schafer
Keyword(s):  
Mammalian Cells ◽  
Chemical Potential ◽  
Basolateral Membrane ◽  
Regulatory Volume Decrease ◽  
Preceding Paper ◽  
Cell Swelling ◽  
Apparent Permeability ◽  
Chemical Potential Difference ◽  
K Concentration ◽  
Volume Decrease

We utilized the microscopic and morphometric procedures described in the preceding paper to examine the role of a swelling-activated dumping of K-salt in the reversal of hyposmotic cell swelling in the perfused proximal nephron. The rate of the regulatory volume decrease that follows cell swelling in dilute solutions was reduced by two maneuvers that attenuate the K+ chemical potential difference across the basolateral membrane; inhibiting the Na+-K+ pump (e.g., with ouabain) and raising the peritubular K+ concentration. The rate of the regulatory volume decrease was also inhibited by peritubular quinine, which blocks K channels and volume regulation for a number of mammalian cells. Additionally, exposure to hyposmotic solutions resulted in a sustained and quinine-sensitive increase in the apparent permeability of the basolateral membrane to K+ salt, which was monitored qualitatively as the rate of cell volume change that was induced by a perturbation in the peritubular K+ concentration. The simplest interpretation of these results is that the reversal of hyposmotic cell swelling in the proximal nephron is referable at least in part to a swelling-activated loss of K-salt and water from the cells.

Ketoconazole blocks organic osmolyte efflux independently of its effect on arachidonic acid conversion

1994 ◽  
Vol 267 (1) ◽  
pp. C266-C271 ◽  
Author(s):  
M. McManus ◽  
C. Serhan ◽  
P. Jackson ◽  
K. Strange
Keyword(s):  
Arachidonic Acid ◽  
Cell Swelling ◽  
C6 Glioma Cells ◽  
Organic Osmolytes ◽  
C6 Cells ◽  
Anion Channels ◽  
Transport Pathways ◽  
Organic Osmolyte ◽  
Osmolyte Efflux ◽  
Cytochrome P 450

Ketoconazole, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate, and gossypol are reported inhibitors of the lipoxygenase (LO) and cytochrome P-450 enzyme systems and are potent blockers of swelling-activated efflux of organic osmolytes and volume-sensitive anion channels in C6 glioma cells. To directly test the hypothesis that LO- or cytochrome P-450-derived products of arachidonic acid (AA) participate in the regulation of these volume-sensitive transport pathways, we incubated C6 cells with [1-14C]AA and observed the extent and profile of its conversion under basal conditions and after acute swelling. High-performance liquid chromatographic analysis revealed that most (70-80%) of the labeled AA remained unchanged with only 6-8% and 10-20% of label converted to LO- [12(S)- and 15(S)-hydroxyeicosatetraenoic acid (12- and 15-HETE)] and cyclooxygenase- [prostaglandin (PG) E2 and PGF2a] derived products, respectively. Leukotrienes and epoxyeicosatrienoic acid compounds were not produced. The conversion profile of [1-14C]AA was not altered substantially by cell swelling. Treatment of cells with the LO-derived products 5-, 12-, and 15-HETE or their immediate metabolic precursors, 5(S)-, 12(S)-, and 15(S)-hydroxyperoxyeicosatetraenoic acid, at 5 microM concentrations did not stimulate efflux of [3H]inositol. In addition, treatment with HETEs did not override the inhibition of efflux observed with the LO-cytochrome P-450 blocker ketoconazole. Whole cell patch-clamp experiments demonstrated that volume-sensitive anion channels, the postulated pathway for organic osmolyte efflux in C6 cells, are rapidly and reversibly blocked by ketoconazole in a fashion suggestive of direct inhibition rather than via interruption of a second messenger pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

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